1H spin-spin relaxation in normal and cataractous human, normal fish and bird eye lenses

A systematic study on nuclear spin-spin relaxation of water protons in human, fish and bird eye lenses/lens nuclei is reported. The purpose of this study is to clarify the real nature of the relaxation processes not describable as a single exponential decay. The characterization of the spin-spin relaxation by a single exponential is commonly used both in literature and in MRI diagnostics. However, in our opinion, this single exponential decay hypothesis is an oversimplification that can lead to the loss of essential information. Our measurements were performed by Carr-Purcell-Meiboom-Gill (CPMG) pulse sequences on human, carp, chicken and turkey eye lenses/lens nuclei. Several hundreds of CPMG echo amplitude were detected and the time-dependence of their decay was determined by careful fitting procedures. Our results clearly rule out the single exponential decay hypothesis for eye lenses: at least two or three decaying components are observed. These phenomena need further investigations: it should be decided which of the relaxation parameters, T2I-s and A(i)-s gives the most characteristic physiological or pathological information. It is claimed that the amplitude ratio of the bound and the free water fraction carries the most characteristic information. During the cataract formation the weight of free water is raised by more than 25%.